Big enough?

I've been looking at the marineland starfire tanks. they have a 3' depth and come in a few lengths a 5' 450 or 6' 500... Would one of these tanks house a pair of Motoros for life or will I be looking at an upgrade? I'm looking at housing my 3 fire eels and a florida gar for sure. possibly a few more gar later on if I can aquire them, but plan on keeping the tank lower stocked as a "show" tank in the house. other then going custom are their any other tanks on the market that might fit the bill otherwise? few more months then I will be able to get this show on the road. Just want to make sure I'm getting my research done right.

Thanks Polish I thought the numbers where off.. but I may have been the one who made the mistake, Thats prolly what I get for posting before my eye-lids have fully opened for the day. Does anyone have other suggestions as to where to procure if you will a glass tank of larger size that would be acceptable for a pair of rays? or am I best off putting in an indoor pond, and putting something else in the "main tank" with the fire eels and gar ( which will all be very respectable size when the rays would be introduced)?